Purification of gases



@et 20, 1959 J. R. WILLIAMS ETAL 2,909,038

PURIFICATION OF GASES Filed Dec. 9, 1955 afrol Qz 3.6

PURIFICATION F GASES Jack R. Williams and Ro'bert A. Kohle, Bartlesville, l Okla., assignors to Phillips Petroleum Company, a corporation of Delaware -Application December 9, 1955, Serial No. "552,1 78 14 Claims. (Cl. 6,2-17) This invention relates to the purification of gases. In one ofits aspects, the invention relates to the removal of an acetylenichydrocarbon from a mixture containing it by a liquid-liquid contact of the said mixture (as a liquid) with a solvent selective for said acetylenic hydrocarbon. In another aspect of the invention, a liquid-liquid selective solvent removal of an acetylenic hydrocarbon is effected by contacting a normally gaseous mixture as a liquid, with a solvent selective to remove from the mixture, while it is a liquid, said acetylenic hydrocarbon. In another of its aspects, the invention relates to a liquid-liquid contact of a liqueeld normally gaseous mixture containing an acetylenic hydrocarbon with a selective solvent for said acetylenic hydrocarbon to recover a solvent rich in said acetylenic hydrocarbon and other unavoidably absorbed or dissolved components of the mixture and ilashing said acetylenic hydrocarbon-rich solvent to remove the said unavoidably absorbed or dissolved components and recycling the said components to a point in the system other than the place at which the liquid-liquid contact absorption is effected. In a still further aspect of the invention, it relates to a combination operation in which a gaseous mixture is liquefied and contacted as a liquid with a liquid which is selective for at least one of the gases constituting said gaseous mixture as it is contained in the liquid which is obtained when the said gases are liquefied, thus to recover, on the one hand, a puriiied gas, as a liquid stream, and a solvent containing dissolved or absorbed therein a gas which has been removed from the said gases to result in the said purified stream.

Itis known to purify gases by contacting the same with a solvent which will selectively absorb from-the gases a component or components which are undesirable therein. Furthermore, it is known to absorb an acetylenic hydrocarbon from a gaseous mixture thereof with other gases by employing various selective solvents including dimethyl formamide. Still further, it is known to take an acetylenic hydrocarbon-rich solvent and to llash the same, returning vapors thus obtained to the absorber.

We have now found that by conducting a liquid-liquid contact absorption or extraction of an acetylenic hydrocarbon from a liquefied mixture of it and other normally gaseous components, employing a selective solvent, that certain -advantages result, as will be more fully set out hereinafter. Furthermore, we have found that the acetylenic hydrocarbon-rich solvent which is thus obtained can be flashed with return of the flashed gases to a point in the system which precedes the said liquid-liquid contact abinvention are apparent from a study of this disclosure,

the drawing, and the disclosure.

According to this invention, a mixture is purified to remove undesirable gases therefrom by contacting the said mixture, as a liquid, with a solvent veffective under the conditions of operation to remove from the said mixture the undesirable constituent thereof. It will be obvious to one skilled in the art in possession of this disclaims which are appended to this closure that the so-called undesirable constituent of said 4 mixture need not necessarily be a constituent which is undesirable elsewhere. Thus, though the constituent is undesirable in the mixture to be purified, the said constituent may have great utility elsewhere. Since the invention applies particularly well to the removal of an `acetylenic hydrocarbon from a normally gaseous mixture, l

it will be described in connection with such a removal.

It is believed clear that Ialkynes, as for example acetylene and methyl acetylene, are materials which possess great utility. By normally gaseous mixture is meant a mixture which is in the gaseous state at atmospheric pressure and normal laboratory temperatures. By the terminology liquefy, liquid-liquid contact, and contacting said mixture as a liquid in liquid-liquid contact with a solid and other similar terminology here and in the claims is `meant only that the normally gaseous mixture has been liqueed by subjecting said mixture to conditions of temsorber to obtain increasedeconomy and effectiveness of from thesaid mixture. Itis another object of this invention topprovide a process for the removal of an 'acetylenic -i hydrocarbon from amixture containing the same. Itis a further object of this invention to lprovide agas puriiication process .of increased economy and eiectiveness.

Other aspects, objects, and the several advantages ofthe liquid mixture. Y

covered'rfrom a vcracking perature and pressure which will liquefy the same. Liquefying a mixture of gases within 'the scope v of this disclosure and appended claims excludes absorption of `said gases, while Vin vgaseous form, into an absorption liquid such as a mineral seal oil, thus resulting in a liquid containing said gases.

Also according to the present invention, there has been provided a combination of steps in the purification of a vnormally gaseous mixture by liquefying the same and A contacting the same with a solvent adapted tovremove undesirable constituents from said liquefied mixture which comprises additionally the flashing ofthe said solvent'to,V

remove certain constituents unavoidably absorbed therein and returning the said constituents to a point in `the process or method which precedes the said liquid-liquid contact absorption.` If the mixture is originallyV a liquid, there is, of course, no need to liquefy the same, `Flashed gaseous constituents will, of course, be returned into the liquid mixture under conditions to become a part of said the feed consists of a mixture of methane, ethane, acetylene, ethylene, propane and propylene. l v Referring now to the drawing which illustratesa specie embodiment of this invention, generally, there arel shown the following principal pieces of equipment. From left to right, the towers are respectively a demethanizer, v

a deethanizer, a deacetylizer anethylene recovery tower. drawing,

or acetylene absorber, and In the lower portion of the there areA shown solvent flashers and a solvent stripper. As will be apparent from the detailed descriptionf which follows, various ancillaryequipment is shown I and described with respect to the-portions of the drawing of illustration only and arenot intended to Abe complete in every of their engineering details. vother equipment which one skilled in the art will understand to be used have been omitted for sake of simplicity.VV Referring now to the drawing, a stream of gases con- Q :taining ethylene and acetylene, such as produced arid yre-l i operation, is first demethanized! 14;by `feeding the saidstre'am'of gases ata pressureof`-ap which are set forth by way Thus, valves, pumps, coolers, heat exchangers and 3 prox'nnately A38`0'poundsf perV square inchabsolute into a demethanizer-operated ata Atop xtemperature of-I-ISOF. Y In the demethanizer, methaneV and any lighter gases are substantially removed from the gases fed thereto. Bottornsfr `rnrthe`l demethnizer are' passed ibyway of 1'conduit 2 and tpressurereducing Lvalve t3 fantasmer Aby. wayof =f conduit 4 into the deethanizer which is maintainedeatlap proximately 27 5' 1pounds-'per`4 isqua're inch `Tabs'`olute"-- and whichlhsla ibottoms temperature -ofl 12"?'1121 v`v In the 1de'-l ethani'z'er,-'C3. hydro'carbonsi VareA removed and withc'irawn asibott'oms through conduit 4a.r`v Ofv'erheadfronti-the de'fA ethanizer is'lpassed -fby wayJof tconduit 5 and eooler`r6 into' overheady reuxfdrumlv The-.temperature maintained inlfthe rerncdrhmiis about' 'l8 FS Redux quantitiesof-- liquid-fromlreuxidrum 7 are piped to a Atray-at orfnear the topfot'ftheI deJeth-a'nize'r byway of-conduitsf*and9.j Production quantities of material-fromlreux drum 7 arepas'sed by Sway of1co'nduit=9 and pump .-10 and further by way of. conduit'flili into the -acetylene'absorber 11d. This absorb'eroperates atl-about 268 vpounds pe`r square'inchf absolute and ismaintained at-litsbottom at approximately 30viand atl 'its'topfatv approximately 60" As s Willfbe understood by those-skilledin the art in possessionsoli-this disclosure, itlcan beloperated at other temperatures* which' 'canbeeven llowen- According to the invention, as'y notedg-this 'absorber Y isloperated as 'a liquid-liquid conl ta'ct'o'r. Thatisfthesabsorber isl substantially liquidfull and-:the '-gases are -also liquid under theconditions' of-its openation; Thef-iadvantagesWof such operation -aredeL scribedlfelsewhere lherein. The overhead fromitheab-h sorber,'in'which dimethyl formamideitDMI-l) isemployed to'ftremoveflaeetylene 'from `the' gases- (which -arerliquid inthe absorber) consistsY principally of ethylene and some eth'ane.I Alsofsome dimethyl formamide may hewn-"- tainedin-y this 'overh'eadewhich isremoved from the ab-- sorber by way ofconduit 12, 'expansion valve 13, and con-y ducted by way of conduit 14 into the ethylene: product recovery'ltower' or fractionator 14a.- Thistower isoper-'ated in this embodiment at a tower 'top-temperature of"g about =65 F. and-`a=bottoms te'rnperatureof about '28 Overhead fr'om thisY tower isi substantiallyacetylene-free ethylene; This Vmaterialis 'removed'as product "by way of conduit- 15` Bottoms consisting sent-ially offethane Vandfsome dimethyl 'forrnamide are taken Efromiithe Atower by-way of conduit;16,"eXpansionA valye-llcondui-t :18 vvand/cooler 19 and-iinally by way otlconduit y2(I-"t0 ethanestorage, not shown.' Anyfseparatefdimethyl formamidephase which collects in cooler -19 is recoveredand reused.4 This dimethylformamide is removed -by-.way offconduit 21.' Returningnowto the' liquid-liquid contact acetylene absorber, bottoms arere; movedJ-by' wayof-"conduit 22 and'passed y'bywvay of ex-v pans'inavlveeZS vvinto, flasher 24,#'Whichis'operated in`this embodimentatapproximately'|10 FQ and'underSO". pounds-'per square'inch 7absolute pressure. Thetempera-- ture firrlfisher -24 isl adjusted `Vby means of heat `exchanger' 22a in conduit 22. In flasher 24,3some'ejthylene,A acety-` lene'and ethane are released and pumped by Way`ofcon-- diiit-'f-ZS;HT conduit 26,'pump 2'7,l and` conduit'28,' conduits 3U^-`andx31`and Valve "32' lto-thedeethanizcer column.` Heat exchanger 129may vbe provided in'conduit 30'fo'r removal ofihatromthe'recycle"gas stream.' Some orall of. the material 4in conduit'r30'can be passed by wayof conduitv Siliandvalve 30h into conduit'fll for return'to the acetylene absorber: OneI oflthe advantages 'of crossover-conduitftl is foundin'placinghe unit on stream." Further,A so'r-rie"or"a1ll `^0f"thev materialin 'conduitl31 canbe 'passed by wayiof crossover conduit 31aand vvalv'e 31b into condu'tSc vI-eregtoo,`the"advantages areas'have just been stated `among othefadvantages which can be recognized by o'neskilled infthe'art." Bottomsfrom asher 24 are passed by wayof conduit 33, expansion valve 34,"and condiiit*35"into" a second flasher 36.? Overhead Afrom flasher 36"'isft`aken` by'way of conduit 37,' "pump 3S,"intoconduit`. Z6fat`id by Away l.of pum'pl'l and c0ndit-28,'etc'., backdo. Y

and sentltofstorage by wayof'conduitl48x The storage isilno'tshownforlisakeoffsimplicity Bottoms romdrum'i?, which consist essentially of dimethyl formamide," are cycled YbyI way of conduit-49 to flasher 36.=- Bottomsfrom the dimethyl formarnide' stripper are removed by way of conduit 50 and passed=by= way ofi-pumpf51, conduit 52, heat exchanger 41, conduit S3, cooler or chiller 54 and conduit 55 into the acetylene absorber 1:1a.

It Willi-be" noted 'that the advantagesof*the-'modus operandiof this invention, especially asl appliedetoeth'f puric'ation of ethylene, jinl the specific embc'xiinent-noted,` are various.' Thus; in viewof vthe liquidliquid contactor absorber e orextractorl operation, very` small relativeA volumes Aofmateria-l'to betreatedfare necessary tti-be pumped and otherwise handled. Acetylene isrecov'ered as -a usable product. The ethylene product -is obtained free 'of acetyleneand therefore the ethylene; whichcanjA be-'usedlior-refrigerationfin the Lprocess or elsewhereg'isf more desirable, especially from `a safety y viewpoint; It will beenoted also'that 'a yliquid feedI is passed' to the ethylene recoveryjtower;l Sucha liquid feed hasm'any advantages yover the feedingfofgas toA suchV a columng as' wili'be understood by-those-skilled in the'art in pose' sessiorrol thisfdisclosure.

Generally, it Will be 'clear to one skilledv inthe art-in possession'eof-this disclosure that the temperature' maybe' different depending' upon -the solvent employed? Also,-` the pressure will depend'upon the temperature' employedx" Still" further;l the pressure will be that which is" necessary l for maintaining substantially/inthe liquid phase thehyl' drocarbon'Whichis'present in those parts of th'e system" in which Aa liquid vhydrocarbon Vphase is' required according to theeinvention. j

It: will be noted that the vapors "which are' taken 'oifl fromdiashersM- 'and 36 are returned 'to the `de"ethani.zer.Y

and' ordinarily' not to 'the' liquidliquid contact'labs'o'rber' in vwhich acetylene is absorbed from'th'e ethylene-con# taining stream^employing 'a liquid dimethyl formamide'. This istalso" an 'important 'characteristic or .feature 'of the present' inventiong which'. provides forV return 0f A'the said4 vaporsfromdhesaid ashers to a .point'in-'the process*or"system.which" precedes the said liquid liquid contact. Heat'elichanger 29".is provided in conduit 301 to 'removethe' heatin the recycle gas stream, since the introductionof thisstre'am directly into conduit 11 would?` lead tovundersirabl'e heating effects in the acetylene abi sorber. However-,tit is apparent 'that the recycle gas in'conduitZS isto be returned to the system through either conduits31 or 31,"the heat of thesstream wilLbe removed in cooler 6." In this case, an advantageous saving in equipment can be realizedby the elimination of heat exchanger 29'.

The following material balance will aid in a more complete understanding 'of 'the embodiment of theinventiom which has been 'described .by reference to the drawing...

Material 'balance (mols'j rPercent Methane Trace to 2 Acetylene 0.4 to 1.5 Ethylene 35 .to 40 Ethane 5 to 15 Propylene 40 to 60 Propane 1 to 2 It will be obvious to thoseskilled in this art that the liquid-liquid contact or extraction step in which `acetylene is separated from the other constituents of the liquefied gases can be effected under widely varying conditionsy which give liquid phase separation. Thus, if refrigeration is available at a temperture lower than 60 1"`.,- say, at '-66" AF. or lower, the extractor can obviously be operated at lower pressures than those which would correspond to the temperatures just mentioned. The, temperature is obviously limited only by the freezing point of 4the solvent used.

With reference to maximum utilization of solvent, the vapor stream in conduit 30, during separation, in one embodiment, is returned to the acetylene absorber by way of conduit 11. It will be noted that even in this event the vapors are not directly returned to the said absorber.

Further, according to the presently `disclosed modus operandi, the product ethylene is not contaminated with DMF or other solvent because said solvent is removed at the foot of the ethylene fractionator.

Finally, another important advantage of the overall system is that the ethylene once liquelied for the liquidliquid contact of the invention is used directly as 'a liquid as a feed to the ethylene fractionator and, therefore, low temperature reflux requirements are reduced. With a vapor feed, it is apparent that the liquefaction within the fractionator would be at the expense off additional low temperature refrigeration required by the column reflux,

condenser.

Although the invention has been described in a specific embodiment with relation to the 'removal of acetylene from a mixture containing it, ethylene and other gases by liquid-liquid contact with dimethyl formamide, it is ob'- viously not limited thereto. For example, it is obvious that other solvents selective for acetylenic hydrocarbons can be used, such as dimethyl sulfoxide, acetone, acetic anhydride,'and dialkyl amides in addition to dimethyl formamide such as diethyl acetamide, diethyl formamide, and the like. Further, other systems comprising different acetylenic hydrocarbons can be processed by this invention. For example, methyle acetylene can-be removed from 'a mixture of it, vpropylene, and other gases with a suitable solvent, for example, dimethyl formamide. Also, ethyl acetylene" and/or vinyl acetylene can -be removed from a mixture comprising butylenes and/or butadiene. Diacetylene can be removed from a normally gaseous mixture by the process of this invention. In addition, the liquid mixture comprising the acetylenic hydrocarbon need not be from a prior fractionation step as shown in the drawing of a specific embodiment but can be used directly las a liquid, for example, from a reaction zone in which a chemical reaction involving an acetylenic hydrocarbon is carried out in liquid phase. Additional selective solvents, systems, and applications of this invention will be apparent to one skilled in the art in possession of this disclosure.

liquid contact.

-It is evident from the foregoing description that the invention is applicable generally to the separation of light hydrocarbons, for example, acetylenic hydrocarbons from other light hydrocarbons, particularly from mixtures containing olefins, which mixtures can also contain parafins.

TheA acetylenic hydrocarbon need not boil close `to the desired pure gas. For example, diacetylene might be the impurity to be removed from a mixture of lower vboiling hydrocarbons. Since it is heat sensitive, distillation may not always be desirable. The diacetylene can readily be removed according to the invention;

Reasonable variation and modification are possible Within the scope .of the foregoing disclosure, drawing, and the appended claims to the invention, the essence of which is that a mixture, ordinarily a normallyr gaseous mixture, is purified to remove the contaminant or other gases therefrom by contacting the said mixture in liquid phase with a solvent adapted to remove said contaminant or other gas therefrom under the conditions of operationY and further characterized in that the contaminant-rich solvent is flashed to remove unavoidably dissolved gaseousy constituents therefrom and then the said unavoidably dissolved removed now gaseous constituents are recycled to' a point in the system Ywhich precedes the said liquidgaseous mixture is treated, as described.

We claim: 1. The removal of a gas from a mixture of gases which are normally gaseous which comprises liquefying Vsaid mixture by subjecting said mixture to conditions of temperature and pressure which will liquefy the same and contacting the said mixture of gases as a liquid with a ksolvent adapted under the conditions of liquid-liquid contact to remove from said mixture a liquefied component recovering on the one hand a stream from which saidV component has been removed and on the other hand'a solvent rich in saidl removed component, flashing said solvent rich in said removed component to remove therefrom portions of said mixture, other than said component gas, which have been unavoidably absorbed during Vthe liquid-liquid contact, to remove from said solvent`the said unavoidably absorbed portions'and returning said. unavoidably absorbed now recovered portions to a point in the system which precedes the said liquid-liquid contact.

2. A method according to claim l wherein the ponent gas is an acetylenic hydrocarbon.

3. A method according to claim 1 wherein the gas mixture to be treated is composed essentially of ethylene and acetylene.

4. The removal of a normally gaseous acetylenic hydrocarbon component from a normally gaseous mixture which comprises subjecting said mixture to conditions 0f temperature and pressure which will liquefy the same and then contacting said mixture as a liquid in a liquidliquid contact with a solvent selective for said acetylenic hydrocarbon so as to solvent extract a substantial propor-l tion of said hydrocarbon component from said mixture while said mixture is maintained under conditions of temperature and pressure which will maintain said mixture as a liquid in the presence of said solvent. i v

5. A method for the recovery of substantially pure ethylene and substantially pure acetylene from a mixture' sorbing medium, recovering acetylene from said absorbing medium, recovering from said contacting a fraction containing essentially ethane and ethylene but not containing acetylene in appreciable quantity, separating the The now greatest advantages and the" presently preferred operation is that inwhich a normally com- 7 ethanehfrom the ethylene and recovering, ethylene substantially' free from ethane.

65A method ,according to claim 5 wherein theabsorh-.f

ing ,medihrisdimethyl 'formamidel 7.!'I`lie removal lof acetylene andethylene from a mixture `ofJ-hydr'ocarbons containing the same. together Vfi.

with-other hydrocarbons Which`comprises demethanizing r said mixture when it contains methane,removingtlahy-l drocarbns from said mixture when such hydrocarbons;

are contained therein,A passing the remainder. of said gasesV under conditions of temperature and pressure which will" liquefy lthe same and maintain the same as a-liquid into a .liquid-liquid contact with a solvent selective to remove acetylene therefrom, obtaining from said -liquid-lic`1`uidv contact an overhead .stream rich in .ethylene and a-.lower stream of '.solve'nt containing. acetylene. and some unavoidablyextracted ethylene, flashing said lower. stream.

to recover therefrom at least a portionof-said ethylene,y

and-returning said rethylene to the system ahead of said liquid-liquid contact.

8l 4The operation of claim 7 vvherein' the shed solvent containing acetylene is stripped to recover acetylene-and the .solvent is recycled to the liquid-liquid Contact step..

9f`A`methodffo'r the recoveryof substantiallypure.

ethylene and substantially pure acetylene from -a mixture' tacting-'said liquid With a liquid-absorbingmedim so as to recover in said medium largely acetylene only dissolved in said medium, recovering from said contactinga fraction containing essentially ethylene and not containing.`

acetylene in appreciable quantity,,separating the ethyleneV from said fraction and recovering lthe same substantially,

free-from acetylene and other gases which originally accompanied it-insaid mixture.

10. -A method for the recovery of vsubstantially pure ethylene and substantially `pure acetylene from a mixture of lgases containing ythe same whch'comprisesfconcentrating into `a liquid form a substantial proportion-of'-` the'ethylene andacetylene present in saidy gases by subjecting 'said 'gases to conditions of ltemperature and -pressure whichwill liquefy the same thus obtaining a liquid,v

contacting said liquid withfa liquid-absorbingmediun so as to recover in said medium largely acetylene only dissolved in said medium, recovering from said contacting a fraction containinges'sentiallyl ethylene and vnot containing acetylene in appreciable quantity, separating the ethylene from saidyfraction, recoveringsthe same substantially free from acetylene and other gases originally lac-` companying it in said mixture, recovering from said liquidabsorbing medium a stream containing acetylene and some ethylene, and returning at least a fraction of said stream containing ,acetylene and vsome ethylene to a.point in theA systemwhich precedes the contacting of the gases in.

liquid form with lsaid medium.

l1. A method according to claim 10 wherein. the absorbingmedium is dimethyl formamide.

12.n Arnethod `for the recovery of substantially/,pure ethyleneand substantially pure acetylene from a mixture of 'gases containing the same together with other gases 8e whichcomprises feedingfsaidgases to a zone vwherein some gases other than acetylene are .removed 'from said gases, then contacting Qthe remainder of said gases under conditions of 'temperature and pressure which willmaintain said `gases in liquid form with. an absorbing medium 'also'. inliquid .fo'rm to recover therefrom substantially only/' ,acetylene dissolved 'in the absorbing-medium, re-l covering la stream ofacetylene containingethylene from saidl absorbing medium, recovering `from said contacting.; a fraction containing essentially ,ethane and ethylene but.. not containing acetylene in appreciable quantity, separat' inghtheethane from the ethylene, recovering the ethylene substantially freetfrom ethane,-and. returning .said-.stream'` of acetylene-containing. ethylene-.to`V a `point in the systemt Y Which-'precedesthe `contact .of .the gases. in `.liquid :formi with said absorbing.-.mediurnW 13 Al method accordingto claim Y 12 wherein the-.- ab-- i sorbing imedium. isdimethyl. formamide.

14.` Theremovalof acetylene and ethylene. from a mixture .ofhydrocarbons .containingrthe same. togetherl with.- other. hydrocarbons. which comprises. .deinethanizing `said mixture whenit conta-ins.metl1ane, rernovingCz; hydrocarbonsfrom said-mixture when such hydrocarbonsare contained therein, passing. the: .remainder of said gases under .conditions .of .temperature .andpressure which vwill maintain. saidgases as a liquid into. a .liquid-liquid contact with afsolvenhseleetive to remove acetylene therefrom, obtaining from .saidl'liquid-liq'uid' contact; .an overhead i stream rich in ethylene and a ldwer stream'of solvent containingcetyleneand.some unavoidably extracted ethylene,.ashingtsaid lower stream to `recover therefrom at least a portion of said ethylene, and returning .said ethylene-to the system .at the. placeat.which"C3`hydrocarbons are removed fromsaid .mixture when suchhydrocarbons are contained therein.

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1. THE REMOVAL OF A GAS FROM A MIXTURE OF GASES WHICH ARE NORMALLY GASEOUS WHICH COMPRISES LIQUEFYING SAID MIXTURE BY SUBJECTING SAID MIXTURE TO CONDITIONS OF TEMPERATURE AND PRESSURE WHICH WILL LIQUELY THE SAME AND CONTACTING THE SAID MIXTURE OF GASES AS A LIQUID WITH A SOLVENT ADAPTED UNDER THE CONDITIONS OF LIQUID-LIQUID CONTACT TO REMOVE FROM SAID MIXTURE A LIQUEFIED COMPONENT RECOVERING ON THE ONE HAND A STREAM FROM WHICH SAID COMPONENT HAS BEEN REMOVED AND ON THE OTHER HAND A SOLVENT RICH IN SAID REMOVED COMPONENT, FLASHING SAID SOLVENT RICH SAID REMOVED COMPONENT TO REMOVE THEREFROM PORTIONS OF SAID MIXTURE, OTHER THAN SAID COMPONENT GAS, WHICH HAVE BEEN UNAVOIDABLY ABSORBED DURING THE 